I read in one of the posts that 70-74 slant/6 engines were 198s. Were they all 198s or both 198 and 225? How can you tell which one you have? I've got a 70 model engine, and a 76 model and wondered what they are? Also wondering about hydraulic lifters. I read that 80 and up engines had hydraulics, is this correct? How can you tell, do the rockers look different?

The 198 was the base (smallest) Slant-6 offered in the North American market from 1970-1974. The 225 was also available in those years.
Start by reading the engine ID numbers, which are stamped on a pad below the frontmost spark plug ('70) below the rearmost spark plug ('76). Your '70 engine could be a 198 or a 225. Your '76 could be a forged-crank 225 or a cast-crank 225, depending on production date.
'81 and up (plus a small number of test engines in '78).
Rockers don't have adjustor screws on them, also the rocker cover is different.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Forgive me if this is a stupid question, but how do you adjust valve lash without adjustor screws?

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1970 four-door Dart, 225/A-904/2.45 gears. 0-60 in twenty three minutes!

Hydraulic lifters eliminate the need for lash adjustments.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Duly noted.

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1970 four-door Dart, 225/A-904/2.45 gears. 0-60 in twenty three minutes!

what is valve lash and what does it do?

Valve lash (also "tappet clearance") is the clearance between the tip of the rocker arm and the tip of the valve stem when the valve is all the way closed and the camshaft lobe under that particular rocker is all the way at its heel. This clearance is necessary so that the valve can close all the way. Too much clearance, and the valves open late and close early. The engine runs noisily, builds excessive crankcase pressure, and loses power. Too little clearance, and the valves open early and close late (or don't close at all), causing rough running, low power and burnt valves.

The slant-6 engines produced before 1981 require periodic tappet clearance adjustment. Use This procedure.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.